1. Field of the Invention
The present invention relates to a neutralization device for an electrical switching unit, such as a contactor, a starter or a contactor breaker, equipped with one or more power poles. The neutralization device is activated when the degree of erosion of the contacts for a pole is greater than a predetermined threshold. The invention also relates to an electrical switching unit including such a neutralization device.
An electrical switching unit such as a contactor has, at each power pole, movable contacts that are separable from stationary contacts, moved using a solenoid to switch an electrical load to be controlled. The pads mounted on the contacts erode more or less with each switching according to the current or voltage load. After a high number of operations, this erosion may lead to failure of the electrical switching unit, the consequences of which may be significant, especially in terms of safety. To prevent such consequences, one solution consists in systematically replacing either the contact pads or the electrical switching unit after a certain number of operations. In order to avoid replacement that is premature or too late, electrical switching units have been equipped with systems indicating to the user the real degree of erosion of the contact pads. In this way, the user is alerted at the desired moment of the end of the lifetime of the electrical unit, which allows failures of the electrical unit and the damages that these failures might cause to be prevented.
2. Related Art
In the patent applications WO 2004/057633, WO 2004/057635 or U.S. Pat. No. 6,225,807 electrical switching units are equipped with devices indicating to a user the degree of erosion of the contact pads of the unit. For example, in the patent application WO 2004/057635 the remaining lifetime of the contactor is determined from the variation in the contact force exerted by the spring in the course of time to hold the movable contacts against the stationary contacts when the contacts are closed. In U.S. Pat. No. 6,225,807 the remaining lifetime of contact pads is determined by calculating a modification of the contact pressure during an operation of opening the contacts.
The systems described in these documents only allow an indication to be given to the user and do not protect against the possible dangers if the unit continues to be used when the contact pads have reached a high degree of erosion.